1. Field of the Invention
The present invention relates to a semiconductor device including a bleeder resistor circuit formed on an SOI (Silicon-On-Insulator) substrate.
2. Description of the Related Art
A semiconductor integrated circuit formed on an SOI substrate is now widely known. In particular, a high-speed MOS transistor which operates in full depletion mode shows more excellent characteristics than those of the conventional MOS transistor formed on a silicon substrate.
A bleeder resistor composed of a plurality of polycrystalline silicon resistors is often used in an analog IC such as a voltage detector. It is however difficult to manufacture an analog IC with high precision since it is difficult to obtain the same resistance in the polycrystalline silicon resistors due to the influence of grains (grain boundaries). An arrangement in which a potential of a conductor arranged over an upper surface or below a lower surface of a polycrystalline silicon resistor is fixed to obtain a desired resistance is known (for example, refer to JP 09-321229 A (FIG. 1)).
The bleeder resistor composed of the plurality of polycrystalline silicon resistors is often used in the conventional analog IC such as the voltage detector, which is formed on the SOI substrate. However, as disclosed in, for example, JP 09-321229 A, even if the potential of each of the polycrystalline silicon resistors is fixed by disposing electrodes on insulating films surround the resistor in vertical directions, the influence of grain boundary is larger and it is difficult to form resistors having the same resistance with high precision. Further, increase in an occupation area of the bleeder resistor region by providing especially contact holes to fix potential is a problem, which leads to an increase in cost of the IC.